Modern inventory systems, such as those in mail order warehouses, supply chain distribution centers, airport luggage systems, and custom-order manufacturing facilities, face significant challenges in responding to requests for inventory items. As inventory systems grow, the challenges of simultaneously completing a large number of packing, storing, and other inventory-related tasks become non-trivial. Expanding the size or capabilities of many inventory systems requires significant changes to existing infrastructure and equipment. As a result, efforts are made to increase the utilization of space bounded by a finite infrastructure by increasing the density of packing in both horizontal and vertical directions. For example, inventory systems are now occasionally split between ground floors and mezzanine levels within a large structure. However, moving inventory items into or out of densely packed storage areas or multilevel storage areas can be inefficient using existing ground-based units or conventional vertical displacement mechanisms like elevators.